Prior to the present invention, various compression devices have been known in the art for applying compressive pressure to a patient's limbs in order to increase blood flow velocity. Particularly useful are the SCD (trademark of The Kendall Company, assignee of the present invention) sequential compression devices providing intermittent pulses of compressed air which sequentially inflate multiple chambers in a sleeve, beginning at the ankle and moving up the leg. This results in a wave-like milking action which empties the veins and results in greatly increased peak blood flow velocity, thus providing a non-invasive method of prophylaxis to reduce the incidence of deep vein thrombosis (DVT). These compression devices find particular use during surgery on patients with high risk conditions such as obesity, advanced age, malignancy, or prior thromboembolism. When a DVT occurs, the valves that are located within the veins of the leg can be damaged, which in turn can cause stasis and high pressure in the veins of the lower leg. Patients who have this condition often have swelling (edema) and tissue breakdown (venous stasis ulcer) in the lower leg. It has also been shown that pneumatic compression can be highly effective in the treatment of such edema and venous ulcers. This treatment is usually performed at home on a daily basis.
Devices of the foregoing description are disclosed in various patents of which the following are illustrative: U.S. Pat. Nos. 4,013,069 and 4,030,488 issued to James H. Hasty; U.S. Pat. No. 4,320,746 issued to Edward J. Arkans and Frank K. Villari; and U.S. Pat. No. 4,938,208 issued to John F. Dye, the last-mentioned patent to John F. Dye being particularly directed to units for home treatment.
In general, the compression devices of the prior art comprise a sleeve having plurality of separate fluid pressure chambers progressively arranged longitudinally along the sleeve from a lower portion of the limb to an upper portion. Means are provided for intermittently forming a pressure pulse within these chambers from a source of pressurized fluid during periodic compression cycles. Preferably, the sleeve provides a compressive pressure gradient against the patient's limbs during these compression cycles which progressively decreases from the lower portion of the limb, e.g. from the ankle to the thigh.
Sequential pneumatic compression devices of the foregoing description applying compression to the lower limb have achieved considerable notoriety and wide acceptance as an effective non-invasive means for preventing deep vein thrombosis and for treating venous stasis ulcers.
They function by applying pneumatic compression sequentially and in gradient levels from ankle to thigh for a predetermined time, e.g. 15 seconds, followed by a period of time, e.g. 45 seconds, when no pressure is applied. The particular time period selected is chosen to be optimum for pushing venous blood out of the leg (during the compression cycle) and to allow arterial blood to refill the leg (during the decompression interval).
It has recently been discovered that it may also be advantageous to apply pneumatic compression to the foot to provide significant venous blood movement therefrom. For example, U.S. Pat. No. 4,702,232 and a division thereof, U.S. Pat. No. 4,841,956, of Arthur M. N. Gardner and Roger H. Fox relate to a device for inducing venous-return flow, which device is intended for use on a impaired human leg. In accordance with the teachings of these patents, the cyclical succession of venous pump action which would occur in normal walking is achieved by involuntarily or artificially activating a foot pump followed by artificially induced separate transient operation of a proximal calf pump and then an artificially induced separate operation of a distal calf pump. As disclosed, the pump actions are achieved by providing inflatable bags or cuffs around the foot and upper and lower calf regions, the inflatable cuffs being separately connected by tubes to a fluid pressure supply means. Each cuff is inflated and then deflated before the next cuff is inflated. Moreover, the cuffs are not inflated sequentially from distal to proximal. The sequence disclosed in the patent of foot pump, proximal calf pump and then distal calf pump does not encourage an effective pumping of blood from the leg.
Stated simply, the task of the present invention is to provide an improved compression device which provides more complete venous emptying by permitting selective application of compression to the plantar venous plexus in the foot and to the leg, thereby more effectively obviating the trapping of blood which can occur in the foot veins, particularly during initial compression, as may be the case with the current sequential compression devices applying no sequential compression to the foot region.